In recent years, there have been proposed and developed various variable valve actuation devices, for example, variable valve timing control devices designed to enhance their control stability and control responsiveness by the use of an electric-motor-driven converter. One such motor-driven converter equipped variable valve actuation device has been disclosed in Japanese Patent Provisional Publication No. 2009-185785 (hereinafter is referred to as “JP2009-185785”), corresponding to U.S. patent application Publication No. US2009/0199801 A1, published on Aug. 13, 2009. In the variable valve timing control device disclosed in JP2009-185785, in order to variably control engine valve timing depending on an engine operating condition, a relative angular phase between a camshaft and a timing sprocket, which sprocket rotates in synchronism with rotation of an engine crankshaft, is changed by reducing the rotational speed of the output shaft of the electric motor by means of a speed reducer constructed by a planetary gear drive.